|Year : 2019 | Volume
| Issue : 1 | Page : 24-30
Dexmeditomedine as an adjuvant reduces the minimum effective anesthetic volume of ropivacaine required for supraclavicular brachial plexus nerve block
Parli Raghavan Ravi, MN Vijai
Department of Anaesthesiology, Command Hospital Air Force, Bengaluru, Karnataka, India
|Date of Submission||02-Jan-2019|
|Date of Acceptance||11-Apr-2019|
|Date of Web Publication||19-Jun-2019|
Gp Capt Parli Raghavan Ravi
Department of Anaesthesiology, Command Hospital Air Force, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Dexmeditomidine has been used as an adjuvant with local anaesthetic amides for supraclavicular brachial plexus block for improving the quality and duration of analgesia. We conducted this study to find out that whether as an adjuvant it reduces the minimum effective anaesthetic concentration (MEAC) and minimum effective anaesthetic volume (MEAV). Materials and Methods: 90 patients undergoing upper limb surgery were randomized into three groups and given ultrasound guided supraclavicular block. Group A received 30 ml of 0.5% Ropivacaine, Group B received 20 ml of 0.5% ropivacaine with 50μgm dexmeditomidine and Group C received 15 ml of 0.5% ropivacaine with 50μgm of dexmeditomidine. The onset of sensory and motor block, the duration of sensory and motor block, quality of analgesia, haemodynamic and sedative parameters were recorded. SPSS software was used for statistical analysis. Results: The onset of sensory block in Group B(9.47±3.54mins) and Group C (12.45±3.86) was faster in comparison to Group A(17.64±5.36) which was statistically significant. The duration of the block was also more in Group B and C in comparison to Group A. The requirement of rescue analgesia was also less in Group B and C. There were no statistically significant changes in the haemodynamic parameters and sedation scores. Although the patients of Group C received lesser volume and dose of ropivacaine than Group B, there was no statistically significant delay in onset or duration of sensory and motor block neither any change in the quality of analgesia. Conclusion: We concluded that 15 ml of ropivacaine with 50μgm of dexmeditomidine is adequate for good quality of analgesia with no compromise on onset of analgesia and duration of block..
Keywords: Ropivacaine, sensory and motor block, supraclavicular brachial plexus block
|How to cite this article:|
Ravi PR, Vijai M N. Dexmeditomedine as an adjuvant reduces the minimum effective anesthetic volume of ropivacaine required for supraclavicular brachial plexus nerve block. J Mar Med Soc 2019;21:24-30
|How to cite this URL:|
Ravi PR, Vijai M N. Dexmeditomedine as an adjuvant reduces the minimum effective anesthetic volume of ropivacaine required for supraclavicular brachial plexus nerve block. J Mar Med Soc [serial online] 2019 [cited 2019 Jul 19];21:24-30. Available from: http://www.marinemedicalsociety.in/text.asp?2019/21/1/24/260656
| Introduction|| |
Brachial plexus block has remained an important tool of the anesthesiologist for decades while performing upper limb surgery not involving the shoulder. With the advent of ultrasound (US), the supraclavicular brachial plexus block has become safer with less complications and failure rates.
Various local anesthetic agents have been used to perform brachial plexus block. Ropivacaine is a long-acting amide local anesthetic agent similar to bupivacaine but with less cardiotoxic effects, providing more prolonged sensory blockade in comparison to motor blockade than bupivacaine.
Various adjuvants have been used for prolongation of the brachial plexus block., Among all of them, one of the most commonly used adjuvants is dexmedetomidine, and it has been studied the for prolongation of the effect of local anesthesia in multiple studies. It is a highly selective α2 agonist compared to counterpart clonidine. It acts on the presynaptic alpha 2 receptors and noradrenergic receptors, wherein it binds and inhibits the release of noradrenaline. Its prolongation of analgesia is not associated with any respiratory depression or deep sedation and has been shown to improve the quality of analgesia both intraoperatively and postoperatively.
Although multiple studies have been done to establish the fact of prolongation of anesthesia with dexmedetomidine;, there are no studies in literature which proves or disproves the role of dexmedetomidine in reducing minimum effective anesthetic volume (MEAV) or minimum effective anesthetic concentration (MEAC) of ropivacaine or any other amide without compromising the quality and duration of surgical and postoperative analgesia. MEAV is the minimum volume of local anesthetic of a given concentration which will provide surgical analgesia in 95% of the patients. MEAC is the minimum concentration of local anesthetic which will provide surgical analgesia in 95% of the patients.
The purpose of this study was to compare the hemodynamic, sedation, and analgesic effect of dexmedetomidine as an adjuvant, and its ability to reduce the MEAV and MEAC of ropivacaine when used in brachial plexus block for upper limb surgery.
Pilot study for determination of minimum effective volume of 0.5% ropivacaine for ultrasound-guided brachial plexus block
In a pilot study using the Massey and Dixon's up-and-down method, the minimum effective volume was calculated in nine volunteers. The initial dose was given as 9 ml per trunk. In case of block failure, volume was increased to 1 ml per trunk. A successful blockade resulted in decrease volume of 1 ml per nerve to the next patient. Successful blockade was defined according to the modified Bromage score (motor block of <2, lack of thermal sensitivity and response to pinprick). The minimum effective volume was calculated (MEAV) as 10 ml of 0.5% ropivacaine per trunk.
| Materials and Methods|| |
This was a randomized controlled study. After approval of the hospital ethics committee, 90 patients undergoing elective surgery of the upper limb below the level of mid-humerus were enrolled in the study [Figure 1]. All the patients were of the American Society of Anesthesiologists (ASA) Grades I or II. The exclusion criteria included preexisting peripheral neuropathies; a known hypersensitivity to the drugs being used in the study; patients with severe cardiac, respiratory, hepatic, or renal disorders; or patient on any alpha-agonist or antagonist therapy. All pregnant patients were also excluded from the study.
A night before the surgery, patients were explained in detail about the procedure and written informed consent was obtained. Using a computer-generated randomization (sealed envelope method), these patients were divided into three groups of 30 patients each and a standard premedication of injection ranitidine 50 mg IV and injection midazolam 1 mg IV was given. The drug was prepared by a senior resident and placed in the block tray. After attaching the standard anesthesia monitors in form of electrocardiogram, peripheral oxygenation (SpO2), noninvasive blood pressure monitor a baseline recording of heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and oxygenation saturation (SpO2) was recorded. After taking adequate aseptic precautions in the operation theater, a supraclavicular approach to identify the brachial plexus with 12 MHz linear probe (Sonosite Turbo Mach) was done. After identifying the brachial plexus, the drug was deposited perineurally equally in following doses in all the three groups of patients:
- Group A: This group received 30 ml of 0.5% ropivacaine
- Group B: This group received 20 ml of 0.5% ropivacaine with 50 μgm of dexmedetomidine
- Group C: This group received 15 ml of 0.5% ropivacaine with 50 μgm of dexmedetomidine.
The spread of the drug injected was done in real time sonographically to achieve a satisfactory spread of drug around the brachial plexus. All the blocks were performed by single anesthesiologist having >7 years of experience in performing US-guided nerve blocks. All the procedures were performed in the regional anesthesia procedure room near to the operation theater. The anesthesiologist who was recording the various parameters of the study (onset, duration of the sensory and motor block, level of sedation, hemodynamic parameters, etc.,) was not involved in the performance of the block and hence was effectively blinded to the procedure and did not know the volume or concentration of drug given to the patient. Sensory and motor block evaluation, along with recording of the vitals, was done every 3 min for the first 15 min, and then every 5 min for the next 15 min or until complete sensory or motor block, whichever was earlier. The sensory block was assessed with the standard pinprick test using a 23-gauge hypodermic needle along the distribution of ulnar, median, radial, and musculocutaneous nerves. The visual analog scores (VAS) were noted (0 – no pain, 2 – mild pain, 5 – moderate pain, and 10 – severe pain). The modified Bromage scale was used to evaluate motor function. The evaluated muscles included the deltoid, biceps, triceps, finger flexors (median nerve), finger extensors (radial nerve), and finger abductors (ulnar nerve). The scoring for motor strength was given as follows: 4 – full strength; 3 – reduced strength, not able to move against resistance; 2 – inability to move against gravity; 1 – tremors or trembling only; and 0 – no movement at all.
The following study parameters were as follows:
- The onset time of sensory block was defined as the time interval between the drug injection and VAS of 4 in the entire four nerve territories. Complete sensory block was considered when the VAS was 0
- Onset time of motor block was defined as the time interval between the drug injection and Bromage scale score of 1 in all the evaluated muscles and complete motor block was considered when the Bromage score was 0
- Duration of sensory block was defined as the time interval from the onset of sensory block to till the time patient complains of pain (VAS of 2). The patient was given rescue analgesics when the pain score was between 2 and 5
- Duration of motor block was defined as the time interval from complete motor block till the time Bromage score was 4
- Quality of anesthesia was graded by the anesthesiologist at the end of surgery with excellent being given a score of 2 and score of 1 being completely unsuccessful with requirement of general anesthesia.
The hemodynamic parameters were recorded every 5 min for the first 2 h, thereafter, it was recorded every 4 h for next 12 h then 6 hourly for next 24 h. A significant change was considered if the HR and blood pressure varied by 20% or there was a drop in saturation below 90%. Any incidences of nausea, vomiting, or skin rash were also recorded. Assessment of sedation was done by the Ramsay sedation score (RSS), as a part of the standard protocol of the hospital for all patients undergoing regional anesthesia. The RSS was also noted down every 5 min for the first 2 h, then every 15 min for the next 6 h. Postoperatively, all the patients received 1 g of injection paracetamol IV at the time of closure of wound, and then whenever the VAS was above 3. The total amount of rescue analgesics required in the first 24 h was noted.
Data were analyzed using SPSS program statistical package for the social sciences software version 17.2 (SPSS Inc., Chicago, USA). Statistical tests which were primarily used were:
- Analysis of variance was used to compare height, weight, body mass index, age, sensory and motor onset time, and duration of surgery among the groups
- Chi-square test for ASA grade, sex ratio, and quality of anesthesia
- Mann–Whitney U-test for VAS and sedation scores
- A power analysis was done keeping alpha level (P < 0.05), which revealed the statistical power for this study as 0.40 for the detection of small effects, whereas the power exceeded 0.95 for detection of large effects. A sample size of 90 was used, which calculated the effect size for the study to be 1.91 with respect to the endpoint of the study (duration of analgesia). This sample size gave the power of study as 1.
| Results|| |
There was no statistical difference among the three study groups with respect to the demographic profile, body mass index, duration of surgery, and ASA grading [Table 1]. The onset of sensory block and motor block was faster in Group B and Group C and was statistically significant in comparison to Group A [Table 2]. Although in Group B, the onset of sensory block (9.47 ± 3.54 min) and motor block (17.64 ± 5.36 min) was faster in comparison to Group C in terms of sensory block (12.45 ± 3.86) and motor block, (19.65 ± 5.36 min) it was not statistically significant. The duration of sensory block (794.34 ± 58.67 min) and motor block (743.48 ± 68.54 min) in Group B was more than Group A (sensory block 356.67 ± 76.45 min, motor block 312.54 ± 38.57 min) and Group C (sensory block 786.35 ± 73.34 min, motor block 712.43 ± 93.48 min). The duration of sensory and motor block in patients in Groups B and C was statistically significant in comparison to Group A; however, it was not so between Group B and C. The duration of analgesia was significantly more in Group B and C (948.32 ± 72.63 min and 970.34 ± 82.34 min) in comparison to Group A (546.32 ± 65.34 min), respectively, and was statistically significant.
The total rescue analgesia required by patients was maximum in Group A patients (4.51 ± 0.54 g), while it was (2.34 ± 0.23 g) for Group B and (2.31 ± 0.33 g) for Group C. The amount of rescue analgesia required was statistically significant in Group A when compared with Group B and C.
The intraoperative hemodynamic parameters were stable in all the three groups of the patients [Table 3]. The HR, SBP, and DBP from 15 min to 240 min (6 h) from the time of injecting the drug were statistically reduced in Group B and C in comparison to Group A. However, the fall was within the 20% limit in the total analysis. Bradycardia was observed in 3 patients in Group B and 2 patients in Group C without any drop in SBP or DBP. One patient was given injection atropine 0.6 mg IV in Group B. However, 2 patients in Group B, 4 patients in Group C, and 1 patient in Group A developed a fall in their blood pressure which responded to fluids and need not require any inotropic support. Three patients in Group A, one in Group B and C required total intravenous anesthesia and were excluded from the study [Figure 1].
There were no significant changes in the mean RSS among the groups, and this was similar with the oxygen saturation, which did not fall significantly in any patient of the group.
| Discussion|| |
Dexmedetomidine has been one of the most studiedadjuvants in anesthesiology.,,, Apart from its analgesic, sedative, hemodynamic, and sympatholytic effects due to its alpha (α)-2 agonists action, multiple animal studies have proven its ability to increase the duration of thermal antinociception and analgesic effect. Studies have also proven it to be neuroprotective, by reducing inflammation and thus decreasing the chances of peripheral nerve injury when mixed with amide local anesthetics. The prolongation of analgesic effect, when combined with amide local anesthetics for various regional and central neuraxial blocks, has been widely studied; however, we did not find any study in literature wherein it reduced the dose requirement of local amides in regional anesthesia without compromising the quality of analgesia and duration of the analgesia. This will help in reducing the dose-related neurotoxicity caused by prolonged exposure of local amides which is dose related.
Ropivacaine has been widely used in various studies for its performance on supraclavicular nerve blocks due to its unique pharmacological properties and lesser side effects. In the study, we used ropivacaine in a concentration of 0.5%. Our reason for using this concentration is supported by the fact that studies have shown that there is no increase in onset of action or duration of analgesia when a concentration of 0.75% is used and lower concentration of 0.25% has been shown to have increased and frequent requirement of supplemental analgesics.,
In the study, we reduced the dose of ropivacaine in patients randomized in Group B to 20 ml and to 15 ml in Group C with addition of dexmedetomidine as an adjuvant by 50 μgm, while Group A received 30 ml of 0.5% ropivacaine. The onset of sensory and motor block and prolongation of duration of anesthesia was more and statistically significant in Groups B and C, in comparison to Group A. Multiple studies using various local amides ropivacaine, bupivacaine, or levobupivacaine, have also demonstrated the same, but in these studies, the volume of local amides used along with dexmedetomidine as an adjuvant wasthe same as in the group which received only the local amides. Our study demonstrated that in spite the fact that the volume and dose of ropivacaine were reduced in Group B and C, the onset of sensory and motor block, and the duration of analgesia requirement increased compared to other Group A.
Further, our study revealed that in spite of reduction of the dose of local amides the requirement of rescue analgesics was not high and was statistically less in comparison to the group receiving ropivacaine alone. This has been demonstrated in other studies using local amides;, however, all these studies had similar dose of ropivacaine mixed with dexmedetomidine as adjuvant. The findings in our study were similar to the hemodynamic parameters and sedation scores in comparison to other studies.,,,
Statistically, reduction of the dose of ropivacaine in Group C (15 ml) patients did not change the onset and duration of motor and sensory block, the duration of analgesia, requirement of rescue analgesics, and maintained the hemodynamic parameters when compared to Group C (20 ml).
Various studies have used various concentration of dexmedetomidine varying from 25 μg to 100 μg to 1 μg/kg, with local amides., Studies with increasing a dose of dexmedetomidine as adjuvant have shown more incidences of bradycardia and hypotension which were statistically significant; however, studies using 50 μg did not report any such complication similar to our study. Studies having a dose of dexmedetomidine <50 μg have equivocal reports on the onset and duration of motor and sensory blocks. Most of the studies had shown results similar to our studies albeit without reduction of dose of local amide. Most of the studies used either nerve stimulator or US to perform the block. Using ultrasonography, the perineural spread of drug can be more controlled and visualized. Fang et al. using US found that the minimum effective anesthetic concentration90 of ropivacaine which will be effective in 90% of the patients for supraclavicular nerve block, was 40 ml of 0.257% (102.8 mg). They did not use dexmedetomidine as adjuvant in their studies. Similar conclusions have been made by Duggan et al. in their study. We used a lesser dose of ropivacaine (100 mg in Group A and 75 mg in Group B) for similar effects. Fredrickson et al. who used different volumes of 0.75% ropivacaine (5, 10 and 20 ml) and 0.375% (20 and 40 ml) for interscalene block found that lower volumes (5 ml of 0.75% ropivacaine and 20 ml of 0.375% ropivacaine) had higher failure rates, while higher concentrations and volume were associated with prolonged duration of analgesia; however, gains in duration of analgesia was insignificant in higher volumes. The, however, did not add any adjuvants in their study. González et al., who used three different concentration of lidocaine for infraclavicular block and Gupta and Hopkins who used different concentration of bupivacaine, found that mass (volume of drug) was the main determinant for the MEAC. However, none of the studies used any adjuvant in their studies. In the study, we found that adding an adjuvant brings down the MEAC and MEAV significantly without compromising the duration and quality of analgesia.
Various studies have risen, concerned regarding the neurotoxicity of local amides, which is dose and volume related. Although ropivacaine is considered least of the neurotoxic in most of the studies, lowering its volume and dose will definitely be beneficial; however, it should not compromise the duration of analgesia. In the study, we found that 15 ml of 0.5% ropivacaine with and adjuvant is enough to provide adequate and good analgesia, and there is no requirement of using higher concentrations or volume of it. Multiple studies have shown the protective effect of dexmedetomidine by decreasing the inflammation around the peripheral nerve. Hence, a combination of ropivacaine and dexmedetomidine will not only have an effect on the rapid onset and a longer analgesic effect but will havea protective effect on the peripheral nerves regarding neurotoxicity.
| Conclusion|| |
Hence, it is important to have a reduced dose of ropivacaine and an ideal adjuvant dose of dexmedetomidine to avoid complications of neurotoxicity due to amides or excess bradycardia, hypotension, and excessive sedation due to dexmedetomidine. We recommend a dose of 15 ml of 0.5% ropivacaine mixed with 50 μg of dexmedetomidine, for US-guided supraclavicular nerve blocks.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]